1. Field of the Invention
The present invention relates to a process for producing a liquid ejection head from which a liquid is ejected. This liquid ejection head includes such an ink jet recording head that an ink is ejected on a recording medium to conduct recording.
2. Description of the Related Art
In an apparatus provided with a liquid ejection head, it has heretofore been conducted to make long the length of an ejection orifice array of the liquid ejection head or to form ejection orifices at a high density for forming a high-quality image at a high speed. The length of the ejection orifice array is made long, whereby an image is completed on one sheet of paper by a few scans, so that the image can be formed at a high speed. The ejection orifices are arranged at a high density, whereby a higher-quality image can be formed.
There are various methods as a method for producing an ejection orifice forming member having an ejection orifice array and a flow path in such a liquid ejection head. In general, the following methods are mentioned.
(A) A method of working an inorganic metal.
(B) A method of directly forming an ejection orifice forming member on a substrate composed of an inorganic material such as Si by a processing process using photolithography.
Description of the method (A) of working the inorganic metal is omitted in the present specification. The photolithography used in the method (B) is a technique in which a circuit of an electronic part or a nozzle is patterned on a photosensitive material using a photomask, and the resultant pattern is transferred.
The photomask is also called a glass dry plate, which is a transparent plate obtained by forming an original pattern to be used in a production process of an electronic part on glass or quartz. In short, the photomask is an original plate upon transferring a pattern on an object of transfer by a transfer technology of the photolithography. In an exposure step, an image of the photomask is transferred on a photosensitive material called a photoresist for every piece. An exposed portion of the photoresist is removed or left making good use of such a property of the photoresist that solubility in a developer is changed by exposure, whereby the thus-treated photoresist becomes a mask for a subsequent dissolving and removing treatment with respect to an object for processing, the treatment being called an etching step. After removal of an unnecessary portion of the object for processing in the etching step is completed, the photoresist is removed with a liquid chemical, whereby a series of steps is completed. Another photoresist is then applied for processing of a next layer, and the same treatments are repeated.
As the photoresist at this time, may be used a liquid photoresist or a film obtained by sandwiching a resist layer of a photo-curable resin between films of polyethylene and polyester, the film being a dry film that is available from Du Pont Co.
In the liquid ejection head, it is applied to a film for improving adhesion between the Si substrate and the ejection orifice forming member as well as to the formation of the ejection orifice forming member, to say nothing of the process of forming a circuit on the Si substrate. In addition, in a microworld of several microns, such as an ejection orifice (also referred to as a nozzle), reduction exposure with a photomask formed with 4 to 5 times magnification in terms of straight line size is utilized without using a same-sized (1:1) photomask with high definition. This large photomask is called a reticle. In recent years, a 6-inch square reticle has been often used for an i-line stepper, which is an aligner of a 1:5 reduction system, in a production of an ejection orifice forming member having an ejection orifice by photolithography. The size of a usable reticle varies according to the performance of an aligner without being limited to the 6-inch square reticle alone and is, for example, 8-inch and 12-inch squares. In the case of 6-inch square, a range in which a pattern is arranged, is 110 mm, and an actual size of a pattern formed varies according to a reduction rate of an optical system. In the case of the 1:5 reduction system, an actual size of a product is up to mm at the longest for one exposure. The above description is regarding an example, and that of another reduction rate is also often used for the i-line stepper.
On the other hand, in recent years, paper pressing technology and high-definition circuit designing have been advanced in printing technology using a liquid ejection head, and so high printing accuracy has been achieved even in a long liquid ejection head having a long ejection orifice array, and the long liquid ejection head has been able to be handled effectively.
On the other hand, when a great number of liquid ejection heads are produced with good accuracy and high efficiency, a process in which a Si substrate is used as a common substrate, a great number of liquid ejection heads are fabricated as chips on the common substrate, and each chip is separated to obtain an individual chipped liquid ejection head is used. According to this process, a common treatment step for the respective chips can be conducted for a great number of chips on the common substrate with good efficiency and at a time or by a repeated operation under the same treatment conditions, and so liquid ejection heads can be produced with high accuracy and good efficiency. Even in this production process of liquid ejection heads using the common substrate, making the length of each chip long has been more and more accelerated from the above-described reason.
Under the foregoing circumstances, a long length chip becomes conspicuous, and so the whole of one chip or all of plural chips cannot fall within a reticle field angle of an aligner in the production of a liquid ejection head using the conventional 6-inch square reticle, so that difficulty is encountered upon fabricating one chip by one exposure.
In some of the prior art techniques, in the case where a long length liquid ejection head is fabricated as in the way described in Japanese Patent Application Laid-Open No. 2003-145769, exposure has been divided in the middle of an ejection orifice array to cope with the above-described problem. In addition, even when exposure is conducted by a stepper having a wide reticle field angle, the same problem is caused again when a chip size is made longer in a next-generation product.
In recent years, an ink jet recording apparatus has been required to conduct recording at a high speed and form a high-quality image, and so ejection orifices of the ink jet recording apparatus have been arranged at a high density, and the length of an ejection orifice array has been made long. Incidentally, a method for producing an ejection orifice forming member includes the above-described methods (A) and (B). Above all, in the method utilizing photolithography with a photosensitive material, the quality of an ejection orifice greatly depends on such a performance as the width of a reticle field angle of an aligner and the accuracy of a lens arranged in an optical path to the reticle. Here, the field angle means a maximum lengthwise and breadthwise width exposable by the aligner. The accuracy of a lens means accuracy in a production stage, such as its curved surface which is nearly horizontal and has a small spherical aberration, the lens being stainless, and so on. Aberration can be corrected by an optical system of the apparatus.
In addition, the size of a chip in which a liquid ejection head is fabricated is also varied, and so even upon the fabrication of one chip, the chip cannot fall within a field angle in an ejection orifice array direction or a direction perpendicular to the ejection orifice array direction by one exposure according to an aligner used, because the length of the chip is made long. It is thus necessary to dividedly conduct the exposure twice or more in some cases. The exposure dividedly conducted twice or more means that the exposure is divided into two or more exposures, because the whole chip cannot be exposed by one exposure when one member is intended to be formed on an Si substrate. In this case, a part that needs to be double exposed is caused due to the alignment accuracy of an aligner. No particular problem is caused so far as an ejection orifice arrangement density is low. However, when the ejection orifice arrangement density is high and a place dividedly exposed twice or more is present near an ejection orifice, there has been a problem that the intended form may not be obtained in some cases due to the telecentric influence of the aligner or partial overexposure. Here, the long length chip means such a chip that a region in which an ejection orifice is arranged can be exposure at one time though the whole chip cannot be exposed at one time, not such a chip that it is too long to a reticle field angle like the prior art literature described above.